As a photoconductive material (a charge generation material or a charge transport material) used for an electrophotographic photosensitive member mounted to an electrophotographic apparatus, an organic photoconductive material has been actively developed. An electrophotographic photosensitive member using an organic photoconductive material generally has a photosensitive layer formed by applying a coating liquid in which an organic photoconductive material and a resin (binding resin) are dissolved or dispersed in a solvent on a support, followed by drying. In addition, the photosensitive layer generally has a lamination type (regular lamination type) structure in which a charge generation layer and a charge transport layer are laminated in this order from a support side.
However, the electrophotographic photosensitive member using an organic photoconductive material has not all the properties required as the electrophotographic photosensitive member. In an electrophotographic process, various materials (hereinafter referred to as “contact members and the like” in some cases) such as a developing powder, a charging member, a cleaning blade, a paper sheet, and a transfer member, are brought into contact with the surface of the electrophotographic photosensitive member. As one of the properties required for the electrophotographic photosensitive member, reduction of degradation in image caused by contact stress with the contact members and the like may be mentioned. In particular, in recent years, as the durability of the electrophotographic photosensitive member has been improved, the continuousness of an effect of reducing degradation in image caused by the above contact stress has been desired.
In order to reduce the above contact stress, a proposal has been made in which a siloxane modified resin having a siloxane structure in its molecular chain is contained in a surface layer of an electrophotographic photosensitive member which is brought into contact with the above various contact members. For example, PTL 1 has disclosed a resin in which a siloxane structure is incorporated in a polycarbonate resin. In addition, PTL 2 has disclosed a technique in which domains are formed in an electrophotographic photosensitive member using a block copolymer resin material having a siloxane structure. As in the above techniques, PTL 3 has also disclosed a technique in which a silicone material in the form of particles is dispersed in a charge transport layer of an electrophotographic photosensitive member, and according to this patent literature, it has been reported that discharge breakdown can be effectively prevented and image degradation (generation of black marks) can be suppressed. In PTL 4 and PTL 5, a polycarbonate resin having a siloxane structure in its side chain has been disclosed.
However, by the electrophotographic photosensitive members disclosed in the above patent literatures, the maintenance of the electrophotographic properties and the continuous reduction of contact stress cannot be simultaneously achieved. In PTL 1, since a polycarbonate resin incorporating a siloxane structure and a polyarylate resin are contained, initial sliding properties are obtained. Although the continuousness of sliding properties is also improved, the degree of the improvement is not satisfactory. In addition, in PTL 1, as a method for imparting continuous sliding properties, a surface layer in which resins are mixed together has been proposed. However, PTL 1 has disclosed that domain formation by resin mixing decreases the optical transmittance and the sensitivity and that the content of a siloxane is controlled so as not to cause the domain formation. In addition, when the content of a siloxane moiety of the polycarbonate resin having a siloxane structure disclosed in PTL 1 was increased, agglomerate of a charge transport material is formed in a polyarylate resin, and as a result, potential stability in a repeated use was degraded in some cases.
The material disclosed in PTL 2 is a resin which includes a component having low surface energy properties and a matrix component, these two components being included in the same resin, and this patent literature has disclosed that since the component having low surface energy properties forms domains, a low surface energy state is formed. Since a siloxane moiety having low surface energy properties has a high surface migration property (interface migration property) and is liable to exist at an interface with a charge generation layer which is adjacent to a charge transport layer, in an electrophotographic photosensitive member comprising a photosensitive layer having a lamination type structure, an increase in potential variation may occur thereby in some cases. In the electrophotographic photosensitive member formed from the material disclosed in PTL 2, the potential variation caused by the above reason also occurred in some cases.
Also in the electrophotographic photosensitive member disclosed in PTL 3 in which the silicone material in the form of particles is dispersed in the charge transport layer, by the surface migration property (interface migration property) as that described above, the potential variation occurred in some cases by the above reason.
In addition, in the case in which when the polycarbonate resin having a siloxane structure in its side chain disclosed in PTL 4 was used for an electrophotographic photosensitive member, a charge transport material was agglomerated in the polycarbonate resin, and the potential stability in a repeated use was degraded in some cases. In PTL 4, in order not to degrade the transparency and the electrical properties, reduction of a siloxane content was investigated; however, the formation of a matrix-domain structure with another resin has not been disclosed. In addition, in PTL 4, impartment of the sliding properties to the electrophotographic photosensitive member has been disclosed, and the initial sliding properties were improved; however, the continuation of the sliding properties in a repeated use was not always satisfactory. In PTL 5, in order not to degrade the heat resistance, reduction of a siloxane content was investigated; however, the formation of a matrix-domain structure with another resin has not been disclosed. In addition, in PTL 5, impartment of the sliding properties to the electrophotographic photosensitive member has been disclosed, and the initial sliding properties were improved; however, the continuation of the sliding properties in a repeated use was not always satisfactory.